Buffering systems for accessing multiple layers of memory in integrated circuits

ABSTRACT

Embodiments of the invention relate generally to data storage and computer memory, and more particularly, to systems, integrated circuits and methods for accessing memory in multiple layers of memory implementing, for example, third dimension memory technology. In a specific embodiment, an integrated circuit is configured to implement write buffers to access multiple layers of memory. For example, the integrated circuit can include memory cells disposed in multiple layers of memory. In one embodiment, the memory cells can be third dimension memory cells. The integrated circuit can also include read buffers that can be sized differently than the write buffers. In at least one embodiment, write buffers can be sized as a function of a write cycle. Each layer of memory can include a plurality of two-terminal memory elements that retain stored data in the absence of power and store data as a plurality of conductivity profiles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application incorporates by reference the following relatedapplication(s): U.S. patent application Ser. No. 11/095,026, filed Mar.30, 2005, U.S. publication number 2006/0171200, and titled “Memory UsingMixed Valence Conductive Oxides,” and U.S. patent application Ser. No.12/001,952, filed Dec. 12, 2007, U.S. publication number 2009/0154232,and titled “Disturb Control Circuits And Methods To Control MemoryDisturbs Among Multiple Layers Of Memory.”

FIELD OF THE INVENTION

Embodiments of the invention relate generally to data storage andcomputer memory, and more particularly, to systems, integrated circuitsand methods to accessing memory cells in multiple layers of memory thatimplement, for example, third dimension memory cell technology.

BACKGROUND OF THE INVENTION

Conventional semiconductor memories typically use access buffers, suchas a write buffer and a read buffer, for exchanging data between aninterface and a memory array. Flash memory devices, for example,ordinarily use one buffer for writing to Flash memory cells and anotherbuffer for reading therefrom. These buffers are usually sized toaccommodate common addressable units of memory, such as a sector or abyte of data. In mass storage applications, Flash memory devices includeNAND-type interfaces that serialize, at least in part, address and dataonto a common bus. Further, Flash-based memories in mass storageapplications typically use a state machine to manage executions ofcommands. While write and read buffers for conventional memories arefunctional, they have limitations. Some of these limitations are linked,at least to some degree, to the underlying semiconductor memorytechnology, such as Flash memory technology.

There are continuing efforts to improve technology for accessing memory.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings. Likereference numerals refer to corresponding parts throughout the severalviews of the drawings. Note that most of the reference numerals includeone or two left-most digits that generally identify the figure thatfirst introduces that reference number. Although the Drawings depictvarious examples of the invention, the invention is not limited by thedepicted examples. Furthermore, the depictions are not necessarily toscale:

FIG. 1 illustrates an integrated circuit implementing a buffering systemthat is configured to access memory cells in multiple memory layers,according to at least one embodiment of the invention;

FIGS. 2A and 2D are diagrams detailing an implementation of a variableprogrammer for a buffering system, according to one embodiment of theinvention;

FIGS. 3A through 3D depict examples of the various size configurationsfor write buffers, according to various embodiments of the invention;

FIG. 4 is a block diagram showing an integrated circuit portionimplementing a buffering system that includes write buffers, accordingto an embodiment of the invention;

FIG. 5 is a block diagram depicting a write override circuit, accordingto an embodiment of the invention;

FIG. 6 is a block diagram depicting an example of an integrated circuitimplementing a write override circuit, according to an embodiment of theinvention;

FIG. 7 is a block diagram showing an integrated circuit portionimplementing a buffering system that includes read buffers, according toan embodiment of the invention; and

FIG. 8 illustrates an integrated circuit implementing a buffering systemthat includes buffers that are disposed in multiple layers of memory,according to at least one embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 depicts an integrated circuit 100 implementing a buffering systemthat is configured to access memory cells in multiple memory layers,according to at least one embodiment of the invention. Integratedcircuit 100 includes a memory 102 and a buffering system 150. As shown,memory 102 includes multiple memory layers 112 formed on top of eachother (e.g., in a Z dimension). Further, memory 102 is divided intopartitions, such as grouping 104 a and grouping 104 b, each of which canbe accessed (e.g., written) separately. Buffering system 150 includes apartition selector 152 and write buffers (“WB0”) 154 and (“WB1”) 156.Write buffers (“WB0”) 154 and (“WB1”) 156 can be sized to write to thepartitions at a specific write speed. In at least one embodiment, thesize of write buffers 154 and 156 can include any amount of data bitsthat are configured to adapt, for example, the write speed to aninterface data rate. In some cases, the amount of data bits can differfrom the smallest addressable unit of memory that constitutes a memorylocation. In another embodiment, the size of write buffers 154 and 156can be configured to sufficiently write to memory cells in a partitionas a function of a rate of change in a programming characteristic, suchas a rate at which a write voltage changes. As such, the sizes of writebuffers 154 and 156 can be configured to maintain a write speed for aspecific rate at which, for example, a write voltage is applied tomemory cells in multiple memory layers 112. The memory cells to whichwrite buffers 154 and 156 write can be located in any plane withinmemory 102. As used herein, a “plane” refers, at least in oneembodiment, to a flat, conceptual surface passing through, for example,the X and Y axes, the Y and Z axes, or the Z and X axes, as well as anysimilar surface that is parallel to any of the aforementioned axes. In aspecific embodiment, the size of write buffers 154 and 156 can be sizeddifferently than the sizes for one or more read buffers, which are notshown.

In view of the foregoing, integrated circuit 100 can implement aspecific amount of data bits to be written per write cycle to reduce,for example, the peak power necessary to program the data bits withoutexceeding a peak power threshold. Thus, integrated circuit 100 can usesmaller write drivers to reduce space or area that otherwise would beconsumed to write larger amounts of data bits. Further, integratedcircuit 100 can use an adjustable size for write buffers 154 and 156 forselecting a specific amount of data bits that are written per writecycle to provide for a write speed that is equivalent to, or issubstantially equivalent to, an interface data rate, especially inimplementations in which the rate at which a write voltage is applied tomemory cells varies the programming time for memory cells in a writecycle. Between interface data rates and write speeds to memory, it isthe latter that usually can determine an interface data rate. By sizingwrite buffers 154 and 156 appropriately, integrated circuit 100 caneffectively set and maintain write speeds independent from modificationsin the rate at which a write voltage is applied to memory cells, which,in turn, increases the time to complete a write cycle.

In some embodiments, integrated circuit 100 can vary the rate at which awrite voltage is applied to reduce instantaneous changes in currentand/or voltage, thereby reducing the “disturb effects,” for example,between memory cells located in, for example, different planes ofmultiple layers 112 of memory 102. Further, integrated circuit 100 canalso vary the rate at which a write voltage increases or decreases toreduce the magnitudes of overshoot voltages when programming memorycells in multiple layers 112 of memory 102, whereby each memory cell canstore multiple states. Disturb effects generally refer to the effects,such as the electrical and/or electromagnetic coupling (or otherwise),on neighboring memory cells not selected for programming when othermemory cells are written. So, integrated circuit 100 can reduce disturbeffects by varying a programming characteristic, such as the writevoltage. In at least embodiment, the size of partitions, such aspartitions 106 a and 106 b, can be sized to reduce overall capacitanceto increase access times to memory cells, and to further reduce disturbeffects by, for example, reducing the amount of memory crossed by oradjacent to an active bit line. In one embodiment, the size of thepartitions in memory 102 can be set to be equivalent to the sizes ofwrite buffers 154 and 156. Note that the size of a partition can includeany amount of memory cells and configured to be separately accessiblefor programming and/or reading. Examples of partitions includepartitions 108, 109 and 110, as well as partitions 104 a and 104 b.

In at least one embodiment, the memory cells of memory 102 may be thirddimension memory cells. A memory can be “third dimension memory” when itis fabricated above other circuitry components, the components usuallyincluding a silicon substrate, polysilicon layers and, typically,metallization layers. By using non-volatile third dimension memoryarrays, memory systems can be vertically configured to reduce die sizeand while preserving overall functionality of an integrated circuit. Inat least one instance, a third dimension cell can be a two-terminalmemory element that changes conductivity as a function of a voltagedifferential between a first terminal and a second terminal. One exampleof third dimension memory is disclosed in U.S. patent application Ser.No. 11/095,026, filed Mar. 30, 2005, U.S. publication number2006/0171200, and titled “Memory Using Mixed Valence Conductive Oxides,”hereby incorporated by reference in its entirety and for all purposes,describes two-terminal memory cells that can be arranged in across-point array. The application describes a two-terminal memoryelement that changes conductivity when exposed to an appropriate voltagedrop across the two terminals. The memory element includes anelectrolytic tunnel barrier and a mixed valence conductive oxide. Thevoltage drop across the electrolytic tunnel barrier causes an electricalfield within the mixed valence conductive oxide that is strong enough tomove oxygen ions out of the mixed valence conductive oxides and into theelectrolytic tunnel barrier. Oxygen depletion causes the mixed valenceconductive oxide to change its valence, which causes a change inconductivity. Both the electrolytic tunnel barrier and the mixed valenceconductive oxide do not need to operate in a silicon substrate, and,therefore, can be fabricated above circuitry being used for otherpurposes (such as selection circuitry). The two-terminal memory elementscan be arranged in a cross-point array such that one terminal iselectrically coupled with an x-direction line and the other terminal iselectrically coupled with a y-direction line. A stacked cross-pointarray consists of multiple cross-point arrays vertically stacked uponone another, sometimes sharing x-direction and y-direction lines betweenlayers, and sometimes having isolated lines. When a first write voltageV_(W1) is applied across the memory element, (typically by applying ½V_(W1) to the x-direction line and ½ −V_(W1) to the y-direction line) itswitches to a low resistive state. When a second write voltage V_(W2) isapplied across the memory element, (typically by applying ½ V_(W2) tothe x-direction line and ½ −V_(W2) to the y-direction line) it switchesto a high resistive state. Typically, memory elements using electrolytictunnel barriers and mixed valence conductive oxides require V_(w1) to beopposite in polarity from V_(W2).

Note that memory 102, which can also be referred to as a “memory array,”in some embodiments, can be implemented using layers 112 of memoryelements arranged in blocks or sub-blocks to store data. By utilizingthird dimension memory, driving voltage requirements can be met by usingmultiple, smaller charge pumps in some cases. Further, multiple,simultaneous accesses of memory elements in a memory array can beperformed. While various types and designs of charge pump circuits canbe used, the implementation of multiple, smaller charge pumps in a thirddimension memory allows for die size to be reduced while improving thecapabilities of integrated circuit 100, such as faster access times forperforming multiple, simultaneous programmable sequences.

Buffering system 150 is configured to implement control signals path 170and data signals path 172. In operation, one control signal from controlsignals path 170 is configured to control partition selector 152 toselect which one of partition lines 160 is to be written. Anothercontrol signal from control signals path 170 can configure write buffer154 to write to multiple layers 112 of memory 102 (e.g., via a firstsubset 162 of partition lines), and can further configure write buffer156 to load data for writing during the next write cycle (e.g., via datasignal path 172). During the next write cycle, the roles of writebuffers 154 and 156 switch. As such, control signals on control signalspath 170 can configure write buffer 154 to write via a second subset 164of partition lines. Write buffers 154 and 156 can be configured to writeand load substantially in synchronicity during a write cycle. Forexample, buffering system 150 can load write buffer 154 at the same time(or at substantially the same time) buffering system 150 uses writebuffer 156 to write to memory 102. Further, the sizes of write buffers154 and 156 can be sized such that the time to load one write buffer issubstantially the same as the time to write to memory cells from theother write buffer. In at least one instance, one write buffer is loadedwith data from data signals path 172 at a write data interface datarate, while the write data is written from the other write buffer at aparticular write speed.

As an example, consider that the write data interface data rate is eightbits per one unit of time, and a write cycle is about four units oftime. Accordingly, at least one write buffer can be configured toinclude thirty-two bits for writing four groups of eight-bit data. Asused herein, the term “interface data rate” generally refers, at leastin some embodiments, to the rate at which an amount of data bits (e.g.,write data bits) are communicated per unit of time via a memoryinterface. As used herein, the term “write speed” generally refers, atleast in some embodiments, to an amount of data bits written to memorycells (e.g., in a partition) per unit time, where such an amount can bean average number of data bits. In accord with the last example,consider that the write speed would be equivalent to 8 bits per unittime for a write buffer that can write 32 bits in one write cyclelasting four units of time. In one embodiment, the “write speed” canrelate to a “programming time,” which, at least in some cases, refers tothe approximate amount of time required to program a memory cell. In atleast one embodiment, a third dimension memory cell can be programmed inabout 500 nanoseconds, or less. In at least one other embodiment, athird dimension memory cell can be programmed in about 50 nanoseconds,or less.

FIG. 2A is a block diagram depicting an example of a buffering system200 implementing a variable programmer, according to one embodiment ofthe invention. As shown, buffering system 200 can include elementsdescribed in FIG. 1, whereby similarly-named elements can haveequivalent structures and/or functions as previously described. Further,buffering system 200 can also include one or more variable programmers202 configured to vary a programming characteristic, such as a voltage,for programming memory cells in one or more partitions in multiplelayers 112 of memory 102. In one embodiment, each variable programmer202 can be configured to modify the states of third dimension memorycells in a partition using a write voltage having a slew rate. Thestates can include a logical one and a logical zero. Or, in some cases,the states can include multiple states, such as a logical “00,” “01,”“10,” and “11,” depending on the resistivity programmed into the thirddimension memory cell. As used herein, the term “slew rate,” at least insome embodiments, refers to the rate of change in a programming voltageover time. The slew rate can, in some cases, refer to an average rate ofchange in programming voltage. A third dimension cell can include atwo-terminal memory element that changes conductivity as a function of avoltage differential between a first terminal and a second terminal. Assuch, each variable programmer 202 can be configured to generate aprogramming voltage for developing a voltage differential in accordancewith the slew rate.

FIG. 2B is a block diagram depicting an example of a variable programmer204 for generating programming voltages for third dimension cells,according to one embodiment of the invention. In this example, variableprogrammer 204 includes an X-line output 203 and a Y-line output 205 forproviding, respectively, a voltage for an X-line (i.e., a row) andanother voltage for a Y-line (i.e., a column). For example, the X-lineoutput 203 and Y-line output 205 can generate either write voltages orread voltages, or both, for a third dimension memory array.

FIG. 2C is a diagram 210 depicting an example of programming voltagesgenerated for third dimension cells, according to one embodiment of theinvention. As shown, X-line output 203 of FIG. 2B provides atriangle-shaped write signal 212 a having a positive voltage during afirst phase, “P1,” of a write cycle, and a triangle-shaped write signal212 b having a negative voltage during a second phase, “P2.” Bycontrast, Y-line output 205 of FIG. 2B provides one triangle-shapedwrite signal during a write cycle. Accordingly, if a logical “1” is tobe written into a memory cell, Y-line output 205 providestriangle-shaped write signal 214 a having a negative voltage during afirst phase, “P1,” of a write cycle. No write signal would be producedin phase P2. But, if a logical “0” is to written, Y-line output 205provides triangle-shaped write signal 214 b having a positive voltageduring a second phase, “P2,” of a write cycle subsequent to phase P1,during which a write voltage can be absent.

FIG. 2D is a diagram 220 showing another example of programming voltagesgenerated for third dimension cells, according to one embodiment of theinvention. As shown, X-line output 203 of FIG. 2B providestriangle-shaped write signal 222, and Y-line output 205 of FIG. 2Bprovides triangle-shaped write signal 224. But note that the phases P1and P2, both of which constitute a write cycle, are longer in time incomparison to the phases in FIG. 2C. Further, triangle-shaped writesignals 222 and 224 have a less steep slope (i.e., rate of change involtage) as do the write signals shown in FIG. 2C. While a less steepslope may be preferable in certain applications, a longer write time isgenerally not preferable. As such, a write buffer 226 can be sized tosize S2 for writing more data bits per write cycle, than, for example,write buffer 216 of FIG. 2C, which is sized at size S1. Note that whileFIGS. 2C and 2D depict triangle waveforms, any kind of waveform, such asa sine waveform or a sawtooth waveform, can be used.

FIGS. 3A through 3D depict examples of the various size configurationsfor write buffers, according to various embodiments of the invention.FIG. 3A depicts a row 300 configured to store bytes 302 of data. In thisexample, write buffer (“WB0”) 304 and write buffer (“WB1”) 306 are eachsized to write eight bits (i.e., a byte) per write cycle. In this case,each partition can be 8 bits wide. In other embodiments, row 300 is asector including about 512 bytes. In cases in which row 300, as asector, is the smallest packet of information that can be read orwritten (i.e., the smallest addressable unit of memory), write buffer304 and write buffer 306 have sizes that differ from sector 300. FIG. 3Bshows a row 310 configured to store bytes 302 of data. In this example,write buffer (“WB0”) 314 and write buffer (“WB1”) 316 are each sized towrite half of the row size. So if row 310 represents a sector, thenwrite buffer 314 and write buffer 316 each can write 256 bits (i.e., 32bytes) per write cycle. In this case, each partition can be 256 bitswide. In other embodiments, write buffer 314 and write buffer 316 eachcan write 512 bytes (i.e., a sector) per write cycle.

FIG. 3C depicts a row 320 configured to store bytes 302 of data in arow, whereby the smallest addressable unit is 8 bits. In this example,write buffer (“WB0”) 324 and write buffer (“WB1”) 326 are each sized towrite multiples of eight bits (e.g., 2 or 4 bytes) per write cycle. FIG.3D illustrates a row 330 configured to store bytes 302 of data in a row,whereby the smallest addressable unit is 8 bits. In this example, writebuffer (“WB0”) 334 and write buffer (“WB1”) 326 are each sized to writeless than eight bits per write cycle. For example, consider that writebuffer 334 and write buffer 336 each can write six bits per write cycle.As such, write buffer 334 and write buffer 336 can write to three bytes,such as byte (“Byte B0”) 312 a, byte (“Byte B1”) 312 b, and byte (“ByteB2”) 312 c, over four write cycles. Thus, write buffer 334 and writebuffer 336 each can be sized to include less bits than a byte, which isthe smallest addressable unit of memory in this example. Accordingly,write buffers in FIGS. 3A through 3D can write any number of bits tofacilitate matching the write speed to an interface data rate. As usedherein, the term “smallest addressable unit” generally refers, at leastin some embodiments, to the fewest number of bits that are accessibleper memory location and/or address. Note that read buffers can be sizedin a similar fashion, according to at least one embodiment of theinvention. Note two that more than two write buffers are possible, and,further, multiple write buffers can be selected to write to memory whileother multiple write buffers are selected to be loaded.

FIG. 4 is a block diagram depicting an integrated circuit portionimplementing a buffering system 401 that includes write buffers,according to an embodiment of the invention. In this example, anintegrated circuit portion 400 includes an interface 410, multiple writebuffers, such as write buffer 420 and write buffer 422, an addressregister (“Reg”) 430, a partition selector 440, an address decoder 432,and X-line driver 442 and a layer 450 a in multiple layers of memoryarray. Layer 450 b is an example of another layer in the multiple layersof memory. Interface 410 includes ports to receive control signals 402(e.g., a write enable signal, a chip select signal, etc.), addresssignals 406 and data signals 404 (e.g., write and/or read data signals).Interface 410 can be configured as either a NOR-type interface or aNAND-type interface. In embodiments in which interface 410 is aNAND-type interface, data signals 404 and address signals 406 aremultiplexed onto a common I/O bus (not shown).

Interface 410 also includes a buffer controller 412 configured to loaddata into a first write buffer (e.g., write buffer 420), and to writedata from a second write buffer (e.g., write buffer 422), whereby buffercontroller 412 synchronizes the loading and writing within an intervalor write cycle. In one embodiment, interface 410 and buffer controller412 cooperate to provide interface control and data signals 414 to writebuffer 420 and write buffer 422, whereby write data of interface controland data signals 414 is transmitted to the buffers in accordance with aninterface data rate. Further, buffer controller 412 is configured toalternately configure write buffer 420 and write buffer 422 torespectively load data at the interface data rate and to write data at awrite speed, which can be substantially the same as the interface datarate. In a specific embodiment, buffer controller 412 can include acounter set to count data bits until a number of the data bits that areloaded into one of the write buffers is equivalent to the size of thebuffer. So when a particular write buffer is full, or is substantiallyfull, buffer controller 412 switches the operation of the write buffers(e.g., from loading to writing, or vice versa).

During a write operation, an address to which data is being written islatched into address register 430. Address register 430 can generate acontrol signal for controlling partition selector 440. Further, addressregister 430 can manage writing data to specific access units, which canbe equivalent to the smallest addressable unit of memory. Or, the accessunits can be larger or smaller. In various embodiments, an access unitcan be the width (i.e., the same number of bits wide) as a partition.For example, access units 452 and 454 can reside in partition 1 (“Pt1”)497 and partition 2 (“Pt2”) 499, respectively. Note that partitions 497and 499 need not extend across the entire length of memory array 450 a.In some embodiments, access units 452 and 454 each can constitute apartition. In at least one embodiment, buffer controller 412 isconfigured to, in whole or in part, convert write data received at amemory interface having an size to accommodate an interface, such as 8bits wide, into access units that can be, for example, 6 bits wide.Buffer controller 412 can also do the same, but in a reverse manner, toconvert read data received as access units from the array sized at, forexample, 6 bits, into read data sized at 8 bits wide, for example, tomatch read data port width of the memory interface. Note that in someembodiments, access unit sizes and/or partition sizes for writing andreading can be different.

For example, if memory array 450 a supported a mass storage application,then its smallest addressable unit of memory can be a sector. Inaddition, address register 430 can pass the address to address decoder432. Further to this example, consider that write buffer 420 and writebuffer 422 are each configured to write four bytes to access unitshaving the same size. Address register 430 can cooperate with buffercontroller 412 to coordinate the writing of each access unit until anentire sector is written. In one write cycle, address register 430 cancontrol partition selector 440 to route write data from write buffer 420to access unit 452, whereas in another write cycle, address register 430can cause partition selector 440 to route write data from write buffer422 to access unit 454. This continues until the sector is written.Similarly, address register 430 can cooperate with buffer controller 412to coordinate the writing of each access unit in a memory that has thebyte as the smallest addressable unit of memory. For example, accessunits 452 and 454 can be four bits wide. As such, access units 452 and454 can constitute one byte, which can be an addressable as a memorylocation. Among other things, address decoder 432 decodes the address toselect both a plane (or a layer) and an X-line associated with a row inmemory array layer 450 a. X-line driver 442 is configured to generatefor a selected X-line a programming voltage signal and a read voltagesignal during a write cycle and a read cycle, respectively. In at leastone instance, write data is transmitted to the write buffers at a writedata interface data rate, which is the interface data rate for writedata. Note that a read data interface data rate is the interface datarate for read data, which can be the same as, or different from, thewrite data interface data rate. In some embodiments, there can be morethan two write buffers.

FIG. 5 is a block diagram depicting a write override circuit 500,according to an embodiment of the invention. In this example, writeoverride circuit 500 is configured to prevent applying a programmingvoltage to a memory cell, such as a third dimension memory cell, if thestate of the data bit stored in the memory cell is the same as the databit being written. This reduces stresses to the memory cell thatotherwise might occur from continuously applying unnecessarilyprogramming voltages. Thus, write override circuit 500 can enhancememory cell reliability, according to one embodiment. In one example,write override circuit 500 can include read-before-write buffer 502 anda comparator 504. Prior to writing data from a write buffer 506 tomemory cells in multiple layers of memory, data from those memory cellsare read from the array into read-before-write buffer 502. Comparator504 determines whether one or more data bits have the same state. If thestates are the same, comparator 504 does not generate a data miscomparesignal 512. As such, write data 514 from write buffer 506 will not bewritten into the array. But if the states differ, then comparator 504generates a data miscompare signal 512, which indicates that the newdata to written is different than the currently-stored data. Thus, datamiscompare signal 512 enables write data 514 to be written into thearray.

FIG. 6 is a block diagram depicting an example of an integrated circuitimplementing a write override circuit, according to an embodiment of theinvention. In this example, an integrated circuit portion 600 includes awrite override circuit 500, a variable programmer circuit 601, an X-linevoltage switch (“Volt SW”) 612, and a Y-line voltage switch (“Volt SW”)610. Integrated circuit portion 600 can also include one memory layer620 in any of the multiple layers of memory, a Y-Line partition selector630, and one or more sense amplifiers (“Sense Amp”) 632. As shown,memory layer 620 includes any number of memory cells 622 a, 622 b, and622 c associated with an X-line 668. In operation, variable programmercircuit 601 is configured to generate a Y-line write voltage at Y-lineoutput 602 and an X-line write voltage at X-line output 604, when writeenable signal 606 is in a state that is indicative of a write operation.Otherwise, variable programmer circuit 601 is configured to generate aY-line read voltage at Y-line output 602 and an X-line read voltage atX-line output 604. Write enable signal 606 can also control operation ofX-line voltage switch 612 and Y-line voltage switch 610 for selecting aspecific memory cell 622 a or subset of memory cells (e.g., constitutingan access unit, or number of bits programmed in a partition during awrite cycle). X-line voltage switch 612, for example, selects X-line 668in response to address (“Addr”) 608.

In one embodiment, integrated circuit portion 600 implements writeoverride circuit 500 in a two-phase process during a write cycle,whereby both phases can occur in parallel or in series. First,integrated circuit portion 600 detects a write to an access unitincluding memory cell 622 a. In response, write buffer 650 communicateswrite data 640 to write override circuit 500 and to Y-line voltageswitch 610. Second, variable programmer circuit 601 generates an X-lineread voltage at X-line output 604, which cause memory cell 622 a to readout a state stored therein. Memory cell 622 a communicates the statedown Y-line 666 to write override circuit 500. If the states are thesame, write override circuit 500 does not generate a data miscomparesignal 642, thereby disabling Y-line voltage switch 610, which, in turn,blocks a Y-line write voltage at Y-line output 602 from accessing memorycell 622 a. As such, write data 640 from write buffer 650 will not bewritten into array 620. This prevents subjecting memory cell 622 a to anunnecessary write voltage, thereby enhancing that cell's reliability.But if the states differ, then write override circuit 500 generates datamiscompare signal 642, which indicates that the new data to written isdifferent than the currently-stored data. Thus, data miscompare signal642 enables Y-line voltage switch 610 to propagate the Y-line writevoltage at Y-line output 602 to memory cell 622 a so that write data 640(or a portion thereof) can be written into array 620.

FIG. 7 is a block diagram depicting an integrated circuit portionimplementing a buffering system 771 that includes read buffers,according to an embodiment of the invention. In this example, anintegrated circuit portion 700 includes an interface 720, bufferingsystem 771 using multiple read buffers, such as read buffer 770 and readbuffer 772, an address register (“Reg”) 430, a partition selector 740,an address decoder 432, and X-line driver 442 and a layer 450 a inmultiple layers of memory array. Interface 720 includes ports to receivecontrol signals 402 (e.g., a write enable signal, a chip select signal,etc.), address signals 406 and data signals 404 (e.g., read dataembodied in read data signals). Integrated circuit portion 700 caninclude elements described in FIG. 4, whereby similarly-named elementshave equivalent structures and/or functions as previously described.Note that interface 720 can be configured as either a NOR-type interfaceor a NAND-type interface. In embodiments in which interface 720 is aNAND-type interface, address signals 406 and data signals 404 aremultiplexed onto a common I/O bus (not shown).

Interface 720 also includes a buffer controller 722 configured tocontrol the reading of data into a first write buffer (e.g., read buffer770), and the transmitting of data from a second write buffer (e.g.,read buffer 772), whereby buffer controller 712 synchronizes the readingand transmitting to a certain interval or read cycle. As used herein,the term “read cycle” generally refers, at least in one embodiment, toan amount of time during which a read buffer is filled, or substantiallyfilled, with read data from layer 450 a, the read data being read outfrom at a particular read speed. As used herein, the term “read speed”generally refers, at least in one embodiment, to the rate at which oneor more data bits are read from memory cells, such as third dimensionmemory cells. In one embodiment, interface 720 and buffer control 712cooperate to provide interface control 724 to read buffer 770 and readbuffer 772 to alternately configure read buffer 770 and read buffer 772to, for example, respectively read data from layer 450 a at a read speedand to transmit the read data at a read data interface data rate. In oneread cycle, read buffer 770 can read the data from access unit 752,whereas in another read cycle, buffer 772 can read the data from accessunit 754. The read data continues being read out via multiplexer (“MUX”)760 and interface 720 to an external terminal (not shown), such as anI/O pin, as read data in data signals 404. In at least one embodiment,buffer controller 722 can include a counter set to count data bits untila number of the data bits that is read into one of the read buffers isequivalent to the size of the read buffer. So when a particular readbuffer is full, or is substantially full, buffer controller 722 switchesthe operation of the read buffers (e.g., from read to transmitting, orvice versa). Note that buffer controller 722 can control via multiplexer760 which of read buffers 770 and 772 will be selected to provide readdata.

Note that in some embodiments, the sizes of read buffers 770 and 772 canbe determined as a function of a read voltage. As read speeds and/orvoltages for memory cells, such as third dimension memory cells, can beless than write speeds and/or voltages for the same cells, then a readcycle can be less than a write cycle. Accordingly, the size of readbuffers 770 and 772 can be different than the size of write buffers. Inat least one embodiment, the size of read buffers 770 and 772 can be thesame size as the write buffers. In some embodiments, there can be morethan two read buffers.

FIG. 8 depicts an integrated circuit 800 implementing a buffering systemcomposed of buffers disposed in multiple layers of memory, according toat least one embodiment of the invention. Integrated circuit 800includes a memory 810 including multiple layers 812 of memory. As shown,multiple layers 812 of memory can include access buffers 802 for abuffering system. Access buffers 802 can include write buffers and/orread buffers. As shown, memory 810 includes multiple memory layers 812formed on top of each other (e.g., in the Z dimension), which, in turn,is formed on a logic layer 820, which can include logic, such as abuffer controller (or a portion thereof) for a buffering system. In viewof the foregoing, a designer can add write and read buffers as accessbuffers 802 in memory 810 without increasing the die size of, forexample, logic layer 820 or the substrate (not shown) upon which logiclayer 820 is formed. Specifically, adding write and read buffers asaccess buffers 802 in multiple layers 812 predominantly affects the Zdimension of integrated circuit 800 rather than the X and Y dimensions.As such, implementation of write and read buffers facilitate bufferingwrite and read data without increasing the die size to include write andread buffers in logic layer 820 or on the substrate.

Further, third dimension memory cells in memory 810 can be produced withequivalent fabrication processes that produce logic layer 820. As such,both can be manufactured in the same or different fabrication plants, or“fabs,” to form integrated circuit 800 on a single substrate. Thisenables a manufacturer to first fabricate logic layer 820 using a CMOSprocess in a first fab, and then port logic layer 820 to a second fab atwhich additional CMOS processing can be used to fabricate multiplememory layers 812 directly on top of logic layer 820. Note that memory810 can be vertically stacked on top of logic layer 820 without anintervening substrate. In at least one embodiment, multiple memorylayers 812 are fabricated to arrange the third dimension memory cells ina stacked cross point array. In particular, two-terminal memory elementscan be arranged in a cross point array such that one terminal iselectrically coupled with an X-direction line and the other terminal iselectrically coupled with a Y-direction line. A stacked cross pointarray includes multiple cross point arrays stacked upon one another,sometimes sharing X-direction and Y-direction lines between layers 812,and sometimes having isolated lines. Both single-layer cross pointarrays and stacked cross point arrays may be arranged as third dimensionmemories.

Embodiments of the invention can be implemented in numerous ways,including as a system, a process, an apparatus, or a series of programinstructions on a computer readable medium such as a computer readablestorage medium or a computer network where the program instructions aresent over optical or electronic communication links. In general, thesteps of disclosed processes may be performed in an arbitrary order,unless otherwise provided in the claims.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the variousembodiments of the invention. However, it will be apparent to oneskilled in the art that specific details are not required in order topractice embodiments of the invention. In fact, this description shouldnot be read to limit any feature or aspect of the present invention toany embodiment; rather features and aspects of one embodiment canreadily be interchanged with other embodiments.

Thus, the foregoing descriptions of specific embodiments of theinvention are presented for purposes of illustration and description.They are not intended to be exhaustive or to limit the invention to theprecise forms disclosed; many alternatives, modifications, equivalents,and variations are possible in view of the above teachings. For thepurpose of clarity, technical material that is known in the technicalfields related to the embodiments has not been described in detail toavoid unnecessarily obscuring the description. Thus, the variousembodiments can be modified within the scope and equivalents of theappended claims.

Further, the embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications;they thereby enable others skilled in the art to best utilize thevarious embodiments with various modifications as are suited to theparticular use contemplated. Notably, not every benefit described hereinneed be realized by each embodiment of the present invention; rather anyspecific embodiment can provide one or more of the advantages related tothe various embodiments of the invention. In the claims, elements and/oroperations do not imply any particular order of operation, unlessexplicitly stated in the claims. It is intended that the followingclaims and their equivalents define the scope of the invention.

What is claimed is:
 1. A buffering system for improved reliability ofnon-Flash two-terminal memory elements, comprising: a plurality ofmemory layers that are vertically stacked upon one another and dividedinto partitions, each memory layer is in direct contact with an adjacentmemory layer; a plurality of re-writable non-volatile memory elementsincluded in each memory layer, each memory element having exactlytwo-terminals and is configured to retain stored data in the absence ofelectrical power, and each memory element operative to store at leastone-bit of data as a plurality of conductivity profiles; a logic layerfabricated on a silicon substrate and including circuitry electricallycoupled with the plurality of re-writable non-volatile memory elementsin the plurality of memory layers, the plurality of memory layers areintegrally fabricated directly on top of and in direct contact with thesilicon substrate; at least one write buffer configured to facilitatewriting to a first subset of partitions during a write cycle; and awrite override circuit included in the circuitry and including acomparator electrically coupled with the write buffer and aread-before-write buffer electrically coupled with sense amp circuitryand the comparator, wherein during a first phase of a write cycle thesense amp circuitry communicates read data from at least one memoryelement to be written to during the write cycle to the read-before-writebuffer, and during a second phase of the write cycle the comparatorcompares the read data with write data stored in the write buffer andgenerates a data miscompare signal if the read data and the write dataare different, the data miscompare signal operative to allow the writedata to be written to the at least one memory element.
 2. The bufferingsystem of claim 1 and further comprising: at least one read bufferconfigured to facilitate reading from a second subset of partitionsduring a read cycle, wherein the at least one read buffer is sizeddifferently than the at least one write buffer.
 3. The buffering systemof claim 1, wherein each memory element changes its conductivity profileas a function of a voltage differential between a first terminal and asecond terminal.
 4. The buffering system of claim 3, wherein thecircuitry includes a variable programmer circuit configured to generatethe voltage differential in accordance with a slew rate.
 5. Thebuffering system of claim 4, wherein the variable programmer circuit isconfigured to generate the voltage differential in the first phase andthe second phase of the write cycle.
 6. The buffering system of claim 1,wherein the circuitry includes an interface configured to transmit datain accordance with an interface rate to the at least one write buffer,and wherein the at least one write buffer is configured to alternatelyload data at the interface rate and to write data at a write speed thatis substantially the same as the interface rate.
 7. The buffering systemof claim 6, wherein the interface further comprises either a NOR-typeinterface or a NAND-type interface.
 8. The buffering system of claim 1,wherein the at least one write buffer is configured to write a specificnumber of bits during the write cycle and the specific number of bitsare selected to perform the write cycle at a peak power that does notexceed a peak power threshold.
 9. The buffering system of claim 1,wherein the write override circuit is configured to prevent writing toone or more memory elements in the plurality of memory layers when thedata to be written to the one or more memory elements is identical tothe read data stored in the read-before-write buffer.
 10. The bufferingsystem of claim 1, wherein one or more of the plurality of memory layersincludes the at least one write buffer.
 11. The buffering system ofclaim 1, wherein subsets of the at least one write buffer are configuredto write and load substantially in synchronicity during the write cycle.12. The buffering system of claim 1, wherein the circuitry includes avariable programming circuit configured to vary a programmingcharacteristic for programming the one or more portions of the pluralityof memory layers.
 13. The buffering system of claim 12, wherein the atleast one write buffer is configured to include an amount of data bitsas a function of a rate of change of the programming characteristic. 14.The buffering system of claim 1, wherein the circuitry includes a buffercontroller configured to synchronize during an interval the loading ofdata into a first write buffer and the writing of data from a secondwrite buffer.
 15. The buffering system of claim 1, wherein the circuitryincludes the at least one write buffer.
 16. The buffering system ofclaim 1 and further comprising: at least one read buffer included in thecircuitry and configured to facilitate reading from a second subset ofpartitions during a read cycle, wherein the at least one read buffer issized differently than the at least one write buffer.
 17. The bufferingsystem of claim 1 and further comprising: at least one read bufferincluded in one or more of the plurality of memory layers and configuredto facilitate reading from a second subset of partitions during a readcycle, wherein the at least one read buffer is sized differently thanthe at least one write buffer.
 18. The buffering system of claim 1,wherein each memory element includes, electrically in series with itstwo-terminals, a mixed valence conductive oxide including mobile oxygenions and an electrolytic tunnel barrier in direct contact with the mixedvalence conductive oxide and having a thickness less than approximately50 Angstroms, the electrolytic tunnel barrier is made from a materialthat is an electrolyte to the mobile oxygen ions and is configured forelectron tunneling during data operations to the memory element.
 19. Thebuffering system of claim 18, wherein a programming operation isoperative to transport a portion of the mobile oxygen ions from themixed valence conductive oxide and into the electrolytic tunnel barrierto store data as a programmed state.
 20. The buffering system of claim18, wherein an erase operation is operative to transport mobile oxygenions that were previously transported to the electrolytic tunnel barrierback into the mixed valence conductive oxide to store data as an erasedstate.